Projectiles for mortars and like projectors



March 6, 1962 P. J. DAWSON ETAL 3,023,704

PROJECTILES FOR MORTARS AND LIKE PROJECTORS Filed July 22, 1958 2Sheets-Sheet 1 FIG. I.

Inventors,

Philip Dawson, Kenn eth 6'. 4 Lawns March 6, 1962 PROJECTILES FORMORTARS AND LIKE PROJECTORS Filed July 22, 1958 6 l6 l4 IS P. J. DAWSONETAL 2 Sheets-Sheet 2 FIG. 3.

FIG. 5.

FIG. 2.

FIG. 4

United States Patent Office 3,023,704 PROJECTILES FOR MORTARS AND LIKEPROJECTORS Philip John Dawson, Beckenham, and Kenneth George AndrewLawrie, London, England, assignors to Minister of Supply, in HerMajestys Government of the United Kingdom ofGreat Britain and NorthernIreland, London, England Filed July- 22, 1958, Ser. No. 750,252 Claimspriority, application Great Britain July 29, 1957 1 Claim. (Cl. 102-94)This invention relates to projectiles for muzzle loading projectors suchas mortars having unrifled barrels.

In order that the projectile shall load easily and slide rapidly downthe barrel of such weapons a comparatively large clearance is necessarybetween the largest circumference of the projectile and the barrel wall.This clearance leads to a loss of propellent energy on firing due toescape of some of the expanding gases through the gap. Round to roundvariation in velocity may also be due in part to this energy loss whichis not necessarily constant, nor is the flow of the escaping gasesnecessarily symmetrical and it may therefore contribute to unsteadinessof the projectile.

The object of the present invention is to reduce the energy loss due toleakage of propellent gases through the clearance gap between theprojectile and the barrel wall and therebyv to increase, for a givenweight of propellant, both the velocity of projection and range of theprojectile and reduce the round to round variation in velocity and hencethe size of the dispersion zone within which a succession of projectilesfired under identical conditions will fall.

With this object in view there is provided in a mortar bomb or likeprojectile, a resilient annular ring of lightweight material sopositioned rearward of the greatest diameter of the projectile that aclearance gap is provided between its outer surface and the projectorbarrel when loaded, the whole or part of which ring is arranged to bemoved by the thrust of expanding propellent gases to such a positionthat the clearance gap between the ring on the projectile and the barrelis sealed to prevent the escape of propellent gases therethrough.

The ring may be of such shape and dimensions that it will distort underthe resultant thrust of the gases and thereby seal the gap, but in itspreferred form the ring is arranged to move bodily forward and at thesame time to expand radially until the gap is tightly sealed.

In its preferred form therefore the resilient ring is arranged to seaton a substantially conical surface on, and coaxial with, the projectilerearward of its greatest diameter in which position a clearance isprovided between the outer surface of the ring and the internal wall ofthe projector barrel, when loaded; and arranged on firing, to be drivenby the thrust of expanding propellent gases, forward along the conicalsurface and to be expanded radially thereby until the outer surface ofthe ring is forced into sealing contact with the barrel wall.

The seating for the ring in its preferred form may be an existing partof the projectile surface or a conical portion formed on that surface.Preferably, however, an annular groove is provided in the projectilewall the base of the groove forming the conical surface. The slope ofthe base of the groove may, if desired, be steeper than the slope of theprojectile surface so that the required amount of radial expansion ofthe ring takes place during a relatively small amount of forwardmovement. If such a groove is used the ring must project sufficientlyabove the projectile surface to provide an adequate rear surface onwhich gas pressure may act to provide the necessary forward movement ofthe ring.

The resilient ring may be of any suitable lightweight material havingadequate elasticity such as, for example neoprene-ebonite orpolyethylene. It must be light enough to be accelerated relative to theprojectile by the resultant thrust acting upon the ring and sufficientlyelastic to be capable of expanding to seal against the projector barrelwithout breaking.

The dimensions of the ring must be such that in its initial position,'before firing, a clearance is provided between the ring and the barrelwall and preferably such that the outer surface of the ring lies whollywithin a cone containing the greatest circumferences of the body andtail of the projectile. The ring must be sufficiently large that whenexpanded by the forward movement it will fit tightly between theprojectile and the barrel wall without danger of being extruded throughthe clearance gap. The danger of extrusion may be lessened by pro vidinga stepped portion on the projectile to limit the forward movement of thering.

Some forms of resilient ring in accordance with the invention will nowbe particularly described with reference to the accompanying drawings inwhich FIGURE 1 is a view of a mortar bomb with a ring seated on itsexisting surface, in position in a portion of the projector barrel andFIGURES 2 to 5 are sections of parts of a bomb wall with alternativedesigns of ring and seating.

In FIGURE 1 a mortar bomb generally designated by the numeral 1comprises a casing 2, an explosive charge '3, a fuze 4, a propellentcharge 5 and a sealing ring 6 seated on the existing surface of the bombcasing 2 and is shown within a portion of the projector barrel 9. Thering 6 has a tapered bore so that its inner surface 7 conformsapproximately to the slope of the surface of the bomb casing 2. The ring6 is positioned some distance rearward of the greatest diameter 8 of thebomb in order to accommodate a ring sufficiently large that when movedforward by pressure of the propellent gases it will seal the gap betweenthe bomb 1 and the barrel wall 9 without danger of extrusion past thegreatest diameter 8 of the bomb 1. The outer diameter of the ring 6 issuch that before firing a clearance is provided between the ring 6 andthe barrel wall 9 for ease of loading, and is preferably such that thering 6 lies wholly within a cone containing the greatest circumferencesof the body and tail of the bomb 1 which cone is indicated by the brokenline 10.

As shown in FIGURES 2 and 3 a modified form of the ring 6 is seated in agroove 11 formed in the surface of the bomb wall 12 immediately rearwardof the greatest diameter 8 of the bomb. The bottom surface 13 of thegroove '11 has a steeper slope than the original surface of the bombwhich is indicated by the chain dotted line 14. The required radialexpansion of the ring 6 is thus obtained by a smaller forward movementthan would be required for a ring seated on the original surface. Thebomb surface 15 immediately rearward of the groove 11 is reduced indiameter in order to expose a greater part of the rear surface 16 of thering 6 to the thrust of the propellent gases. The ring 6 shown in FIGURE3 has a concave rear surface 16. The forward face of the groove providesa step to aid in avoiding extrusion of the ring 6 past the greatestdiameter 8 of the bomb.

Alternatively the resilient ring 6 could be of U-shaped or part U-shapedcross-section as shown in FIGURES 4 and 5 respectively, and attached tothe projectile in such a manner as to form a rearwardly facing channel17 around the projectile wall 12. The inner wall of the channel would beformed by the inner arm of the U in the case of the U-shapedcross-section shown in FIG- URE 4 and by the projectile wall in the caseof the part U-shaped cross-section shown in FIGURE 5. The expandinggases, in addition to driving the ring forward,

Patented Mar. 6, 1962 would exert pressure inside the channel to forceits outer wall radially outward into contact with the wall of theprojector barrel to assist in sealing the clearance gap betweenprojectile and barrel wall. The outer arm of the U must be thick enoughto avoid excessive distortion before sealing occurs.

On ejection from the muzzle of the projector the ring is freed from therestraint applied by the projector wall so that it may either break orexpand further as it is forced forward beyond the greatest diameter ofthe projectile and blown clear of the projectile by the propellent gaseswhich at that point travel faster-than the projectile. Once clear of thethrust of propellent gas the light ring or pieces thereof are subjectedto air drag forces and are rapidly retarded and fall away from thetrajectory of the projectile which, freed from the ring, has a goodballistic shape. The ring or fragments thereof travel only a shortdistance and, owing to their lightness and low velocity, constitute verylittle danger to personnel or equipment.

Trials have shown that mortar bombs modified to incorporate thisinvention are more accurate and have a considerably higher projectionvelocity and longer range than unmodified bombs fired under the sameconditions.

We claim:

The combination comprising an unrified mortar barrel, a projectile to befired in said barrel, said projectile including a rearwardly taperingbody, an explosive charge in said body and a tail assembly attachedrearwardly to said body, there being a circumferential groove formed onthe tapering portion of said body, said groove being disposedsubstantially rearwardly from the largest diameter of said body andhaving spaced forward and rearward vertical walls and a rearwardlyinclining bottom surface, said rearward vertical wall rising to a heightless than said outer tapering surface whereby a rearwardly and upwardlyinclining surface is formed on said tapering body of said projectile,and a resilient ring having a width substantially less than the lengthof said groove, said ring also having a conical bore and an outersurface parallel to the longitudinal axis of said barrel, said ringbeing normally seated at the rearward end of said groove, at which pointthe outer circumference of said ring assumes a smaller diameter than thelargest diameter of said body to provide a clearance gap between saidring and the inner surface of said barrel, said ring adapted to moveforward in said groove and upward in said conical bottom surface thereofupon escape of pro pellent gases of said charge and pressure thereofagainst the rearward face of said ring to expand the latter against theinner surface of said barrel and seal said clearance gap.

References Cited in the file of this patent UNITED STATES PATENTS

